Internal combustion engines of an automobile may utilize an engine control unit (ECU) for electronically controlling engine operation. For example, the ECU may control the engine ignition system the engine as well as other vehicle or engine components, and may also be coupled to a plurality of sensors. In one example, the ECU may be located near or in the engine compartment such that significant heat energy generated by the engine and related components may be transferred to the ECU. As such, it is possible that there may an undesirable temperature rise due to heat buildup in the ECU, which may in turn cause degradation of the ECU and thus engine or other vehicle operation. Further, this heat buildup may be exacerbated by conduction or other transfer of heat from the systems adjacent to an enclosed space in which the ECU is located, and by the heat generated from the ECU itself.
To control or reduce ECU temperature, various forms of heat management may be used. One approach aims at cooling the ECU, either passively or actively. Another approach aims at reducing the amount of heat generated by the ECU. In one example approach aimed at reducing heat generated by the ECU, fuel injection of a diesel engine using piezo-electric fuel injectors is utilized. Specifically, a diesel engine controller with an integrated piezo fuel injector (with a piezo stack) driver circuitry may generate considerable heat in the ECU and contribute approximately 50% to 60% of the total heat generated by a typical diesel ECU. The heat buildup may be reduced by turning off non-essential drivers that dissipate heat when they are energized. The drivers may control systems that are not essential for vehicle/system operation. Also, the drivers controlling the fuel supply to the engine cylinders may themselves be used to reduce heat generation by operating engine at part load with a reduced fuel supply to all of the cylinders or shutting off fuel supply to selected cylinders. Such an approach is described in U.S. Pat. No. 6,655,326.
However, the inventors herein have recognized that reducing engine load, power, or torque, while useful under some conditions, may result in decreased drive feel under other conditions. For example, an operator's perception of drive performance may be significantly reduced if the vehicle is unable to substantially meet power demands under some conditions. Further, if fuel is shut off to selected cylinders, engine vibration may also increase to a more noticeable level, further decreasing customer drive feel.
The above issues may be at least partially addressed by varying (e.g., reducing or limiting) a number of injections per cylinder event during conditions of ECU over-temperature. For example, conditions of ECU over-temperature may include operation at a high engine speeds (which may produce more heat in the ECU), operation at high engine loads, (which may produce engine system heat that may be transferred to the ECU enclosure), operation at high ambient temperature (e.g., greater than 80 degrees F., for example), and/or operation at high measured temperatures in or near the ECU.
In one particular example, the adjustment in a number of injections may be managed in such a way as to continue to deliver the required total fuel amount at appropriate timing. In this case, engine operation may continue to produce a sufficient output torque or load by maintaining sufficient fuel injection with a reduced number of injections. For example, multiple pilot injections may be combined into a fewer number of injections or to a single injection, and/or a split main injection may be combined into a single injection. Further, pilot injection(s) may be foregone before the main injection (and the main injection increased), or post injections may be inhibited by deferring operations in which such post injections are utilized.
In this way, it may be possible to at least reduce heat generated in the ECU during selected conditions. If desired, additional actions may be taken such as increasing airflow in or around the ECU and/or its enclosure, or performing other actions.